The Department of Mechanical, Materials, and Aerospace Engineering MMAE 593 Seminar Series featuring guest speaker Kapil Chauhan, Senior Lecturer in the School of Civil Engineering at the University of Sydney, Australia. Chauhan will present “Higher Order Moments of Scalar Within a Plume in a Turbulent Boundary Layer.” This event is open to the public and will take place on Wednesday, October 29, from 12:45–1:45 p.m. in Stuart Building, room 104.

Abstract

This talk will discuss the statistical nature of instantaneous scalar concentration in an elevated point-source plume (neutral or buoyant) dispersing within a turbulent boundary layer. Using high-frequency long-duration experimental measurements, the gamma distribution is extensively validated as the appropriate probability density function of concentration, particularly at large scalar magnitudes. The two-parameter gamma distribution is shown to capture the PDF at all locations across the plume. The classical similarity of the mean and root-mean-square (RMS) concentration, often expressed through a Gaussian form, is recovered through an equivalent similarity of the scale and shape parameters of the gamma distribution. In addition, the gamma distribution accurately reproduces the previously observed skewness–kurtosis relationship and the 99th percentile of the instantaneous concentration signal. Extended similarity is demonstrated for the third- and higher-order central moments and standardised central moments from the experimental data, with the framework of the gamma distribution also analytically extended to these statistics. The results emphasise the importance of achieving statistical convergence for the intermittent concentration signal, which is directly influenced by finite sampling times in a measurement. The results establish the gamma distribution as a consistent and unified model for all scalar concentration statistics in elevated point source plumes within a turbulent boundary layer, with physical arguments supporting the observations.

Biography

Kapil Chauhan is a Senior Lecturer in the School of Civil Engineering at the University of Sydney, Australia. He received his bachelor’s degree in mechanical engineering from the Maharaja Sayajirao University, Baroda, India, in 2000. Thereafter, he obtained a master’s and PhD in Mechanical and Aerospace engineering from the Illinois Institute of Technology, Chicago, in 2003 and 2007, respectively. His research interests are in turbulent wall-bounded flows, pollutant transport, urban heat islands, natural convection, and wind engineering. Dr Chauhan’s expertise lies in measurement and experimental techniques, data analysis, and data-driven investigation of flow phenomena. Dr Chauhan is currently on a sabbatical at Illinois Institute of Technology, Chicago, until December 2025.